The objectives of this research will be to study immunological reactions to a fibrosarcoma in syngeneic rats. This tumor has been developed as a result of transformation of Buffalo rat embryonic fibroblasts with Herpes virus. We have a unique situation in which one cell line of transformed cells is non-oncogenic, but it is immunogeneic and exposure to this line prior to challenge with the tumorigenic line prevents the development of tumors. We shall be able to study the mechanisms responsible for the regression of established tumors, and establish criteria for the identification and quantitation of tumor associated antigens against which animals respond, without the burden of the presence of an existing tumor. This will be accomplished with a quantitative immunoperoxidase assay for membrane antigens and the staphylococcal protein A immunoprecipitation methodology. Membrane antigens will also be assayed using micro-complement fixation methodology and immunofluourescence. Studies of adoptive immunity will be accomplished using lymphocytes from animals immunized with different cells (T-REF-G2 or RFS or REF). The different cell lines will be maintained in tissue culture, and measurement of immune reactivity will also be accomplished using 1) antibody-complement-dependent cytotoxicity studies; 2) lymphocyte cytotoxicity studies based upon 51Cr release from labeled fibrosarcoma cells; 3) and a lymphocyte target interaction assay.